Teeth whitening: what works and what does not

Why teeth darken

There are two kinds of discolouration, and they need completely different treatment. EXTERNAL stains sit on the enamel surface and come from coffee, tea, red wine, smoking. INTERNAL ones are inside the tooth structure: caused by age (enamel thins and the yellower dentine shows through), old trauma, or certain medication taken in childhood.

The distinction matters a lot: external stains come off with a professional cleaning, no whitening involved. Internal ones need a whitening agent that penetrates the tooth.

What actually works

In-office professional whitening uses high-concentration peroxide, applied under the dentist supervision with the gums protected. It is the fastest and most predictable method.

At-home whitening with custom trays, made from an impression of your teeth, uses a lower concentration worn a few hours a day for one to two weeks. It takes longer, but the result is comparable and often more even.

Over-the-counter „whitening" pastes do not whiten chemically: they contain abrasives that remove surface stains. Useful for maintenance, but they do not change the actual shade of the tooth.

What NOT to do

Baking soda, activated charcoal, lemon, vinegar: all circulate online as „natural whitening". All are either abrasive or acidic, and once enamel is gone it does NOT grow back. The long-term result is the opposite of what you wanted: more sensitive, yellower teeth, because the dentine underneath shows through.

Cheap online kits with one-size-fits-all trays let the gel reach the gums and can cause chemical burns. The tray has to be made for your teeth.

When whitening is not suitable

Whitening only acts on natural tooth structure. Crowns, veneers and tooth-coloured fillings do NOT change colour, so after whitening they can stand out as noticeably darker. If you have restorations in the front, whitening is planned first, then the restorations are remade to the new shade.

It is postponed if you have untreated decay, inflamed gums or marked sensitivity: the agent would reach where it should not, and it would hurt. That is why any proper whitening starts with a consultation, not with the treatment itself.

How long the result lasts

Generally from a few months to two or three years, depending on your diet and whether you smoke. The first 48 hours matter most: the tooth is more porous and absorbs pigment easily, so avoid coffee, red wine, tomato sauce and tobacco.

Temporary sensitivity after whitening is normal and settles within a few days. If it persists, tell your dentist: the concentration or the schedule can be adjusted.